1. Field of Invention
The present invention relates to a grease gun, and more particularly to a grease gun comprising a greasing pumping arrangement with enhanced plunger unit for injecting oil out of the grease gun.
2. Description of Related Art
A conventional pumping arrangement for a grease gun usually comprises a motor having a driving shaft, a yoke mounted in a housing for reciprocating movement in the housing, and a plunger mounted in the housing for reciprocating movement of the plunger in the housing so as to inject oil out of the grease gun.
Conventionally, the yoke usually has an exterior surface and a slot formed thereon, whilst the plunger has a head connecting with the slot so that the reciprocating movement of the yoke will drive the plunger to move in the same reciprocating manner for injecting the oil out of the grease gun.
A main disadvantage of this conventional pumping arrangement is that the plunger is easy to be broken. During a typical oil pumping cycle, the plunger is driven to move in a reciprocating manner along an oil injection channel of the grease gun. This means at the moment the plunger is driven to move in different direction (i.e. from upward movement to downward movement, or vice versa), the driving force from the yoke will mainly concentrate at the point of connection between the plunger and the yoke i.e. the head. Therefore, the plunger is easily broken at the head so as to render the entire grease gun unworkable.
Another disadvantage of the above-mentioned conventional grease gun is that the pumping arrangement is usually powered by a motor which is eccentrically and operatively connected with the yoke so that when a driving shaft of the motor is rotating, the yoke is driven to move in the reciprocating manner. Thus, in order to control the rate of pumping oil at the plunger, it is necessary to incorporate a gear unit between the driving shaft and the yoke so that a desirable or selectable rate of dispensing oil from the grease gun can be achieved. The gear unit usually comprises an operation driver having a driving surface operatively connected with the driving shaft of the motor, an opposed driven surface, and a driving pin extended from the driven surface to connect with the yoke. Thus, when the motor rotates, it drives the operation driver to rotate which in turn drive the yoke moving in the above-mentioned reciprocating manner.
The housing in which the yoke is mounted usually has an annular collar wherein the operation driver is rotatably mounted therein via a ball bearing assembly. The disadvantage of this gear unit and the annular collar is that there exists a substantial energy loss during power transmission between the motor and the operation driver via the ball bearing assembly. One may solve this problem by adding lubricating oil at the annular collar for reducing a friction between the ball bearing assembly and the operation driver, but this not only causes substantial inconvenience to the grease gun manufacturer, but also leads to unstable performance of the grease gun as a whole.